Method for controlling the temperature of metal lances in molten baths



Sept. 22, 1970 r v N. J. THEMELIS 5 METHOD FOR CONTROLLING THETEMPERATURE OF METAL LANCES IN MOLTEN BATES Original Filed March 3, 19674 Sheets-Sheet 1 In a w N cTl N I n 11 II n I! u n n HIHTIHI! V G? V (DNI on n INVENTOR NICKOLAS J. THEMELIS' Sept. 22, 1970 N. J. THEMELIS3,529,955 5 METHOD FOR CONTROLLING THE TEMPERATURE UP METAL LANCES INMOLTEN BATHS Original Filed March 5, 1967 4 Sheets-Sheet 2 lllllllINVENTOR NICKOLAS J. THEMELIS W 9M; 1 W

p 1970 N. J. THEMELIS 3,529,955

METHOD FOR CONTROLLING THE TEMPERATURE OF METAL LANCES IN MOLTEN BATHSOriginal Filed March 5, 1967 4 $heet$*5heet' 5 INVENTOR NICKOLAS J.THEMELI Sept. 22, 1970 N. J. THEMELIS 3,529,955

METHOD FOR CONTROLLING THE TEMPERATURE OF METAL LANCE-S IN MOLTEN BATHSOriginal Filed March 5, 1967 4 sheets-Sheet 4 FIGS INVENTOR NICKOLAS J.THEM ELIS United States Patent U.S. CI. 75-60 5 Claims ABSTRACT OF THEDISCLOSURE A water-cooled lance which may be used in the treatment ofmolten metal and which may be inserted beneath the surface of the metal.The lance structure provides a passage for gases and a passage for acoolant such as Water. The water vaporizes as it contacts the hot lancebody and so acts as a cooling medium and the gas and water vapour areadmixed as they pass through the lance body and enter the molten metalas a gaseous mixture.

This is a division of application Ser. No. 627,466, filed Mar. 31, 1967.

This invention relates generally to a method and apparatus forcontrolling the temperature of metal lances in molten baths.

The major problem in introducing gases in molten metal baths forpurposes of refining or converting has been that irrespective of theflow of gas through the lance, the heat transfer from the bath to thelance greatly exceeds the possible heat transfer from the lance to thegas stream within it. As an example, a steel lance exposed to a furnaceatmosphere of 2400 F. may absorb a maximum heat input of 100,000B.t.u./hr. ft. of exposed surface. The same lance, when submerged in abath of molten copper at 2200 F., absorbs an estimated 400,000 to800,000 B.t.u./hr. ft.

This enormous heat transfer rate in the molten bath is due to the factthat the conductivity of the liquid material is extremely high and alsoto the fact that the bath is usually superheated to at least 100 to 200F. above its melting point and, therefore, constitutes a practicallyinfinite source of heat due to the strong convection currents existingin the bath. On the other hand, for convection between the lance walland the gas stream flowing through the lance at sonic, or evensupersonic gas velocities, the maximum heat transfer rates that can beachieved are in the order of 30,000 to 60,000 B.t.u./hr. ftF. It can,therefore, be seen that it is almost impossible to prevent the lancewall from reaching the temperature of the bath even at the highestpossible flow rate of gas through it, due to the limitation of the heattransfer coefficient by convection between the wall and the gas.Consequently, soon after the lance has been introduced into the bath, itreaches the temperature of the latter and because of the strongvibration caused by the gas injected in the bath, the lance is very soonbroken up.

This problem has appeared to be insurmountable, since when used with agas flow alone, even the best qualities of stainless steels and alloylances available have very 3,529,955 Patented Sept. 22, 1970 littlestrength in the temperature of molten copper baths and none at all inmolten steel. The way in which this obstacle has been overcome in steelrefining by the new oxygen lance technique for steel refining, is toavoid immersing the lance into the bath and also to provide the lancewith a water-cooled jacket. However, in order for this method ofinjection to be effective, it is required that the oxygen emerges fromthe lance: at very high velocities and also that the lance is kept at asafe distance above the bath; these factors have a pronounced effect onthe efficiency utilization of oxygen gas.

In the case of copper processing where the gas must be introduced belowthe surface, the use of lances has met with complete failure and hasprevented the adoption of gas injection techniques into stationaryfurnaces not equipped with refractory tuyeres. In particular, failure ofthe lances has prevented their use in the deoxidation of anode copper. I

The present invention relates to an effective method for overcoming thisproblem and allowing the use of, for example, mild steel or other metalpipes for injecting gases in molten baths.

The lance of the present invention may be used generally for introducinggases into molten metal at high temperatures. In a process ofdeoxidizing copper by hydrocarbon gases, steam and hydrocarbon gases,such as propane and butane, may be mixed and reacted in the lance of thepresent invention. The steam may be replaced by water which is bothvaporized and reacted in the same lance. The benefit of mixing waterinstead of steam is that the lance can be kept cooler making it possibleto use ordinary mild steel pipes for introducing various gases intomolten metals at high temperatures.

Advantages of the invention over previous water-cooled lances, such aswater-cooled sheathed lances or the lance disclosed in US. Pat. No.3,269,829 include the presence of a very advantageous safety aspect.Since the cooling water is atomized at a location outside the bath therecan be no danger of structural failure of the lance or accidentaldischarge of a volume of water suificient to cause an explosion incontact with the molten bath. Therefore, the tip of the present lancecan be immersed in the liquid bath, since a failure of the tip will notaffect the formation of the fine water spray. All other types ofwater-cooled lance referred to above cannot be immersed in the liquidand must be kept at a safe distance above the bath.

In the drawings:

FIG. 1 is a side elevation of a rotary anode furnace with a cut-awaysection showing a lance of the present invention disposed therein.

FIG. 2 is a side view of a reverberatory anode furnace showing threelances in position in openings of the furnace.

FIG. 3 is a cross-section showing the atomizing nozzle of the lance ofthe present invention.

FIG. 4 is a section of a reverberatory furnace with a lance extendingthrough a side port thereof into the melt.

FIG. 5 is a cut-away section of the lance showing the flow of water-gasmixture therein.

Broadly speaking the invention relates to a method and apparatus forcontrolling the temperature of pipes or other lancing devices, used forinjecting a gas into a molten bath, by introducing a finely dividedspray of water into the gas stream thereby greatly enhancing the heattransfer rate between the wall of the lancing device and the gas stream,and maintaining the lance at a temperature below the temperature of thebath, thus preventing fracture or dissolution of the lance material.This method and apparatus may be used in copper refining, either for theoxidation of blister copper or for reducing with gaseous reagents,converting of copper, refining of steel by oxidation or other means, andany other process or scheme where it is necessary to inject a gas streaminto a molten bath of metal, matte, or slag.

The invention is based on the consideration that the heat transfercoefficient between the wall and the gas stream must be increasedconsiderably in order to remove the heat received by the outside wall ofthe lance. This is achieved by introducing a very fine spray of water inthe gas stream at the inlet of the lance located outside the furnace.The size of the spray droplets is preferably less than 100 microns. Apneumatic nozzle is used which disperses a relatively low flow of waterfor example (30 gal./ hr.) into the gas stream in the form of very finedroplets which, when they collide with the wall of the lance, absorb alarge amount of heat by evaporation and then are reflected back into themain stream, much in the same way as a water droplet falling on a hotplate and bouncing on it until it is completely evaporated. The waterflow rate required will depend on the characteristics of heat transferfrom the liquid bath to the lance (temperature of the bath, lancediameter, thermal conductivity, viscosity, specific heat and density ofthe liquid bath).

In this way, the heat transfer between the gas stream and the lance isincreased enormously since the heat transfer coefficient is not any moreone between gas and Wall, but between droplet and wall, which haspractically infinite capacity as a heat sink.

FIG. 1 shows a typical rotary furnace A as used in copper refining. Thistype of furnace is supported on rollers 21 and may be rotated by asuitable motor connected to a wing gear 22. Steam is brought to thefurnace via a pipe 1 and is controlled by a pressure regulator 2 whichkeeps the steam in a loader pipe 4 at a constant pressure. Steam feed toeach lance is controlled by individual valves 3 and is connected to thelance with a flexible hose 5. A hydrocarbon, such as propane or butane,is brought to the furnace via pipe 7 and controlled by a main valve 8.The feed to each lance from a common loader pipe 10 is also controlledby individual valves 9 and connected to the lance by flexible hose 11.The lance assembly consists of a mixing T 6 into which the steam andhydrocarbon is introduced, lance hanger 15, lance bushing 12 and lance14. The lance slip-bushing 12 allows the lance to be manually ormechanically rotated periodically through 180 about the lance axis inorder to compensate for upward bending of the lance tip. The lancehanger is designed to suspend the lance at the proper angle for maximumdepth of lance orifice 17 under the melt surface 19. The whole assemblyis suspended to a suitable support by a hook 16 and cable or rope 24.

The lances in FIG. 1 are shown introduced through openings 18 in the endwalls 13 of the furnace. However, it it also understood that the lancemay be introduced through any openings in the furnace that are foundsuitable, such as openings around the cylindrical shell of the furnace23.

FIG. is a section of the lance of the present invention as it isintroduced into a metal melt 20. Water or other liquid such as naphthais delivered through an inlet tube 34 and end adapter 35 to a mixing andatomizing nozzle 36 and into the lance 14 through an orifice 37. The gasto be introduced into the molten metal is delivered to the lance 14through an opening 33 in a mixing T 6 and passes through the atomizingand mixing nozzle 36 into the lance 14 through orifice 38. The orifices38 are so shaped and dimensioned that water enters the lance 14 in theform of a fine spray. As the mixture of water droplets and gases passthrough the lance 14, in the process of copper deoxidation, the water isvaporized and reacts with the hydrocarbon gases in the lower hot sectionof the lance. It should be understood that gases other than hydrocarbonsmay be used when the purpose of adding water is solely to cool thelance. It should also be understood that the method used for the lanceis only applicable when water is not detrimental to the particularprocess for which the lance is used. The resulting gases or gassteammixtures enter the molten metal through lance orifice 17 and risethrough the melt 20 to the liquid metal surface 19 in the form ofbubbles. Treatment of the melt 20 may consist of either a reactionbetween one, some, or all of the gases entering the melt and someimpurity of the metal itself, such as in the removal of oxygen frommolten copper, or the gases introduced may only act to remove otherdissolved gases in the melt such as in common degassing processes.

The present lance has been tested in the gaseous atmosphere of an anodefurnace at temperatures of about 2300 F when a water flow rate of fivegallons per hour was found sufficient to maintain the pipe below 1800 F.at its tip; the corresponding gas flow rate was 30 s.c.f.m. of propane.The lance Was also tested under the extreme conditions prevailing whenthe lance is immersed to a distance of approximately four feet in a bathof molten copper when the required water flow rate was about 20 gal./hr.for the same gas flow rate of 30 s.c.f.m. of propane.

It should be noted that the present method of cooling the lance byintroducing a finely atomized spray of water affords great flexibilityin controlling that part of the lance which in operation is submerged inthe furnace melt, since it is possible, by introducing more or lesswater, to increase or decrease the temperature at the tip of the lanceas desired.

At the same time, since the metal of the lance can be kept at arelatively low and safe temperature, this invention dispenses with thenecessity of using expensive or extremely strong stainless steels forlancing applications. In the example discussed previously herein, a mildsteel pipe was introduced at an angle into the molten copper to a depthof two feet (corresponding length about four feet) and was subjected tointense conditions of vibration by introducing an overall gas rate ofs.c.f.m. which resulted in very intense mixing conditions in the 'bathand vibration of the lance. Yet, two hours after the lance wasintroduced in the furnace, it was still operating at the same depthwithout showing any adverse effects of attack by the liquid bath orfatigue fracture.

It is clearly apparent from the foregoing that the lance of the presentinvention represents a significant advance in the art.

I claim:

1. In a method of cooling a lance for use under high temperatureconditions in the treatment of molten material in which at least a partof the lance must be submerged beneath the surface of a mass of moltenmaterial, the steps of:

(a) directing a flow of a reformable hydrocarbon gas to a feed chamberon said lance,

(b) directing a flow of coolant liquid into the body of said lance,

(c) exhausting the flow of said reformable hydrocarbon gas from saidfeed chamber against the flow of coolant liquid as it is introduced intothe lance body,

((1) whereby the coolant liquid is dispersed into liquid droplets bycontact with the flow of the reformable hydrocarbon gas, said dropletsbeing caused to impinge in random fashion against the inner periphery ofsaid lance body,

(e) exhausting the gaseous mixture so formed from the submerged tip ofthe lance into the mass of molten material,

(f) whereby the lance structure is effectively cooled in operation.

2. A method as claimed in claim 1 in which said gas is selected from thegroup consisting of methane, ethane, propane and butane.

3. A method of cooling as claimed in claim 1 wherein the coolant liquidis water.

4. A method as claimed in claim 1 wherein the coolant 5 liquid is anaphtha.

5. The method as claimed in claim 1 wherein the size of said droplets isless than 100 microns.

References Cited UNITED STATES PATENTS FOREIGN PATENTS Great Britain.

L. DEWAYNE RUTLEDGE, Primary Examiner 10 J. E. LEGRU, Assistant ExaminerUS. Cl. X.R.

